Random breast swelling 10 years post implants. Advice?

Hi. Thanks for posting your questions.
It sounds like your breast swelling may be hormone related, given they occur in relation to your menstrual cycle. You have done the right thing in getting it assessed with an MRI, and making arrangement to see a plastic surgeon.
One thing which has come to light in recent years is the awareness of ALCL (anaplastic large cell lymphoma). This is a breast-implant related cancer, and one of the signs of this condition is fluid collection and swelling in the affected breast, although the swelling doesn't come and go and is usually one-sided.
All the very best.
Dr Ray Goh